The present invention relates to detection systems by echoes of the radar or sonar type in which an angular sector is the source of electromagnet or ultrasonic radiation transmissions. The determination of the content of the sector follows from the detection and detailed analysis of the signals reflected by the points of the space which were irradiated or insonified. This analysis supplies information on the angular position and distance of the targets. On the basis of this information, it is possible to form on the screen of a cathode ray tube an image representing the scanned sector. The distance of a target from the transmission - reception system is a function of the time elapsing between the transmission of a pulse and the reception of the echo corresponding thereto. The angular position of the target may depend on the directivity of the transmission and/or reception means. The invention more particularly relates to echo detection systems in which reception involves the use of two receivers, whilst the waves are simultaneously received by a system of radiating elements.
Such an association of transmission and reception means has already been proposed in U.S. Patent No. 3,716,824 granted on Feb. 13, 1976. This U.S. Pat. describes a sonar apparatus in which two receivers form a reception channel, whose directivity involves a fan-like lobe arrangement. A line of transmitters supplied by a pulse-modulated monochromatic carrier supplies a very selective insonification of the sector to be monitored, which only covers one of the reception lobes. In this procedure, monitoring is essentially of a punctiform nature and much less extensive than the angular sector in which the reception means can detect the echoes. This system can only supply a detailed image of the sea bed by an appropriate mechanical scanning because only a single channel is used on transimission and reception.